The Rated Life, Bp of an LED light source is different from the Lumen Maintenance Life, Lp, and is an essential reliability value that is required by luminaire manufacturers.
Firstly, let’s see the definition of Rated life, BP.
The rated life of a light source is defined as “The life value assigned to a particular type lamp. This is commonly a statistically determined estimate of median operational life.” (as per ANSI/IES RP-16). The statistical measure for the rated life is designated Bp and is measured in hours, where p is a percentage.
For example, a B50 rated life of 50,000 hours means that 50% of the tested products have lasted 50,000 hours without failure. B50 is also known as the products’ rated average life. If a product has a B10 rated life of 50,000 hours, this means that only 10% of tested products failed within 50,000 hours, so the product should last much longer than a product with a B50 rated life of 50,000 hours. If a product has a B70 rated life of 50,000 hours, this means that up to 70% of tested products failed within 50,000 hours, so the product last much shorter than a product with a B50 rated life of 50,000 hours.
Rated Lumen Maintenance Life, Lp
Rated lumen maintenance life is defined as “the elapsed operating time over which an LED light source will maintain the percentage (p) of its initial light output.” It is measured in hours with an associated percentage of light output, noted as Lp.
For example, L70 of 50,000 hours means that the tested LEDs produce 70% of the initial light output at 50,000 hours. If an LED has L50 of 50,000 hours, its lumen output depreciates faster than one with L70 of 50,000 hours. L90 of 50,000 hours means that the tested LEDs produce 90% of the initial light output at 50,000 hours.
That leads to some new terms like “L70” and “B50.” L70 refers to lumen depreciation to 70% of initial lumen output; stated conversely, it indicates 70% lumen maintenance. “B” specs add a target statistical confidence interval. Thus, B50 indicates no more than 50% of a sample of LED devices would be expected to have their light output drop below a target lumen maintenance level. B10 would mean no more than 10% of the sample met that L standard within the given time.